This study provides a combined experimental and computational investigation into the structure and impact of the cation interdiffusion layer that appears at the gadolinium doped ceria (GDC)/yttria stabilized zirconia (YSZ) interface in solid oxide electrolysis cells (SOECs). Scanning transmission electron microscopy (STEM) illustrates that a similar to 0.4 mu m interdiffusion layer (IDL) with an intermixed cation distribution and fine grain size forms upon sintering. STEM identifies that the interdiffusion layer exists in the cubic fluorite structure despite changes in cation composition. The interdiffusion layer microstructure formed during sintering does not change during SOEC testing at either 1.3V or heightened voltage pulse testing. Modeling predicts that ionic conductivity may decrease in the interdiffusion layer due to Coulombic trapping between mobile oxygen vacancies and excess Gd3+ acceptor dopants. Yet, the density and continuous nature of the layer should benefit cell stability by substantially reducing the formation of SrZrO3, which is corroborated by STEM and Synchrotron X-ray diffraction (XRD). We conclude that the interdiffusion layer acts as a beneficial barrier to Sr diffusion, when operating in a regime where electrolyte void formation is not observed.

The native surface oxide of plutonium plays a critical role in ensuring the stability and safe storage of the underlying metal; consequently, understanding the role of defects and impurities in determining the properties of the oxide layer is critical. Here, we use hybrid density-functional theory calculations to evaluate the electronic structure and defect chemistry of PuO2, the most stable of the native oxide phases, including both native and extrinsic defects. We find that oxygen vacancies (VO) form readily in PuO2, as do polarons. Electron polarons (eta-) are the lowest-energy acceptor species in PuO2, while the charge compensating donor species will shift from VO under O-poor conditions to hole polarons (eta+) under O-rich conditions. Nitrogen and fluorine can substitute readily for oxygen atoms under O-poor conditions, while fluorine can also incorporate in an interstitial configuration (Fi-) under more O-rich conditions. Carbon and chlorine incorporation in PuO2 will be very limited. We also evaluate the kinetic barriers for oxygen-related defects, which we find to diffuse readily when present. Our results provide valuable insights into the critical role and variable chemistry of point defects and impurities in PuO2, which in turn have important implications for the safe storage of the underlying metal layer. In short, exposure of freshly prepared plutonium to reactive nitrogen- and fluorine-containing contaminants should be avoided, while carbon- or chlorine-containing contaminants are less likely to incorporate readily into the oxide.

We study the formation energies of iron impurities in δ-Pu within spin–orbital-polarized density functional theory (SOP-DFT). The thermodynamic solubility limit of iron in δ-Pu is calculated, indicating low miscibility. We show that surprisingly, Fe impurities at equilibrium are almost equally likely to occupy octahedral interstitial sites or substitutional sites, with slight preference for the former. In contrast, we find the energy of the tetrahedral interstitial Fe to be nearly 1 eV higher than the octahedral one. We explore the energy landscape for Fe impurity hopping diffusion and conclude that Fe impurities in δ-Pu are divided into two populations: (i) Immobile substitutional Fe impurities and (ii) highly mobile interstitial Fe impurities. The latter, (ii), migrate between octahedral interstitial sites with an energy barrier of around 0.2 eV. The energy barrier for exchange between the two populations is calculated to exceed 0.7 eV. Finally, we discuss the role of magnetic order on the impurity energetics.

Nanocrystals—including quantum dots and metallic nanoparticles—offer tunable electronic and optical properties that make them promising building blocks for next-generation devices. However, scalable and controllable assembly methods are needed to translate these properties into functional materials. Here, we present electrophoretic deposition (EPD) as a rapid and versatile technique for assembling nanocrystal films and superlattices across a range of compositions, ligand chemistries, film thicknesses, and substrate geometries. By tuning the deposition parameters and combining EPD with in-solution ligand exchange and solvent engineering, we access both disordered, dense films and ordered superlattices with thicknesses ranging from tens of nanometers to several microns. In-situ quartz crystal microbalance measurements provide quantitative insight into deposition kinetics, enabling precise control over film growth rates from 1 to 100 nm/s, competitive with vapor deposition technologies. We demonstrate that nanocrystal ordering can be achieved with long or short surface ligands, and that conformal coating of textured and non-planar substrates is readily achievable. This electric field–driven approach overcomes limitations of conventional solvent-based assembly, enabling the scalable fabrication of nanocrystal-based materials with tailored structure and properties for optoelectronic and sensing applications. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. Figure 1

Polyhedral borane salts are highly tunable compounds with the potential to be used as solid electrolytes due to their high Li and Na superionic conductivity and relatively wide electrochemical stability window. In considering their application to all solid-state batteries, their mechanical properties play a critical role in their operation due to stresses the solid electrolyte is subjected to during battery operation. Density functional theory (DFT) calculations have provided an initial assessment of bulk and elastic moduli for some selected boron cluster solid electrolytes, but direct measurements are still scarce. In this paper, we report the elastic moduli and hardnesses of LiCB11H12, LiCB9H10, NaCB11H12, and NaCB9H10 for the first time using nanoindentation continuous stiffness method (CSM) measurements under inert atmosphere. Experimental modulus values ranging 8.8-12.3 GPa and hardness values ranging 0.15-0.38 GPa are lower than that of other inorganic solidstate electrolytes such as oxide- and sulfide-based solid electrolytes. DFT calculations on the expected moduli of these compounds are also presented and discussed. Analysis of the indentation plasticity index reveals that these compounds have higher plasticity index compared to other common oxide and sulfide solid electrolytes. According to the calculated Pugh's ratio, all compounds in this study except LiCB11H12 are considered ductile.

We present anab initiofree energy model derived from a fully relativistic density functional theory (DFT) electronic structure with dynamic magnetism forδ-plutonium (face-centered cubic, fcc). The DFT model is extended with orbital-orbital interaction in a parameter free orbital polarization (OP) mechanism consistent with previous modeling of plutonium. Gibbs free energy is built from components associated with the temperature dependence of the electronic structure and the corresponding electronic entropy, lattice vibrations within an anharmonic lattice dynamics model, and dynamical fluctuations of the magnetization density, i.e. magnetic fluctuations. The fluctuation model consists of transverse and longitudinal modes driven by temperature induced excitations of the DFT + OP electronic structure. Theab initiomodel thus incorporates fluctuating states beyond the electronic ground state. Thanks to the dynamic magnetism, the theory predicts excellent thermodynamic properties and a Gibbs free energy in accord with CALPHAD and semi-empirical modeling developed from the thermodynamic observables. The magnetic fluctuations further explain anomalous behaviors of the thermal expansion in plutonium. Specifically, a thermal expansion for theδ-plutonium system turning from positive to negative at temperatures above room temperature, a tendency for gallium to reduce and remove the negative thermal expansion depending on composition, and a positive thermal expansion for the high temperatureϵphase.

Understanding the onset of degradation in the air electrode within solid oxide electrolysis cells (SOECs), and the subsequent impact on cell performance, is a critical step in mitigating the performance losses and stability issues of SOECs. In an effort to identify early onset degradation phenomena, SOECs were characterized as fabricated and after testing potentiostatically at 1.3 V for 1000 h at 750 °C. SOEC air electrodes composed of a 1:1 composite of La0.6Sr0.4Co0.2Fe0.8O3-δ (6428-LSCF) and Gd0.1Ce0.9O1.95 (GDC) were studied using synchrotron X-ray diffraction (XRD), scanning transmission electron microscopy coupled with energy dispersive X-ray spectroscopy (STEM-EDS), and X-ray absorption near-edge spectroscopy (XANES) to evaluate the changes in the air electrode structurally and chemically. These techniques show the migration of Sr species from the air electrode through pores in the GDC barrier layer, progressing to the electrolyte boundary, where it accumulates and reacts with (Zr0.84Y0.16)O2-δ (YSZ) to form SrZrO3. Microscopy results are paired with atomistic simulations to better understand the relationship between the thermodynamic instability of 6428-LSCF and cell fabrication/testing conditions. First-principles calculations reveal that LSCF-6428 is not stable during cell manufacturing and testing conditions, which supports the experimental identification of secondary phases in both as-fabricated and tested cells. Together, these results demonstrate that the challenging environments encountered by SOECs during cell manufacturing and operation lead to instabilities of the target 6428-LSCF anode material and underscore the need for more durable, high-performing SOEC components.

Cesium bismuth bromide (CBB) has garnered considerable attention as a vacancy-ordered layered perovskite with notable optoelectronic applications. However, its use as a light source has been limited due to its weak photoluminescence (PL). Here, we demonstrate metal intercalation as a novel approach to engineer the room-temperature PL of CBB using experimental and computational methods. Ag, when introduced into CBB, occupies vacant sites in the spacer region, forming octahedral coordination with surrounding Br anions. First-principles density functional theory calculations reveal that intercalated Ag represents the most energetically stable Ag species compared to other potential forms, such as Ag substituting Bi. The intercalated Ag forms a strong polaronic trap state close to the conduction band minimum and quickly captures photoexcited electrons with holes remaining in CBB layers, leading to the formation of a bound interlayer exciton, or BIE. The radiative recombination of this BIE exhibits bright room-temperature PL at 600 nm and a decay time of 38.6 ns, 35 times greater than that of free excitons, originating from the spatial separation of photocarriers by half a unit cell separation distance. The BIE as a new form of interlayer exciton is expected to inspire new research directions for vacancy-ordered perovskites.

The increasing need for global hydrogen ideally depends on low-cost 1$/kg green hydrogen. The DOE’s Energy Earthshot initiative aims to reduce the cost of green hydrogen to achieve this goal in a decade. There are a number of pathways of which solid oxide electrolysis cells (SOECs) are one of the most attractive1. SOECs have high demonstrated efficiency for hydrogen production without precious metal catalysts but at present with limited lifetimes2–4. SOEC’s have a layered structure consisting of an LSCF-GDC composite cathode (La0.6Sr0.4Co0.2Fe0.8O3-δ / gadolinium doped ceria), a GDC barrier layer, YSZ (yttrium stabilized zirconia) electrolyte, and Ni-YSZ anode support layer. This structure exhibits various degradation mechanisms initiating at both the air and fuel electrode at high operating temperatures predominately at the interfaces5,6. Understanding the mechanisms behind cell degradation and their potential effects on cell performance is critical to reach hydrogen Earthshot goals. There has been significant focus on the coarsening of Ni in the fuel electrode and advancement made in reducing its negative effects on cell performance over time 7. Another significant mechanism is due to the degradation of LSCF at temperatures above 550 °C 8. As LSCF degrades, Sr migrates from the structure and becomes mobile throughout the cell. This poses problems as it reaches the electrolyte and forms SrZrO3 which causes both ohmic losses and potential mechanical failure9. This study focuses on the initiation of this mechanism and its progression in the break in period of the cell. Extensive characterization of early-onset degradation is achieved through SEM (Scanning Electron Microscopy), STEM EDS (Scanning Transmission Electron Microscopy), XANES (X-ray Absorption Near Edge Structure) and Synchrotron XRD (X-ray Diffraction). These techniques are then paired with first principles calculations of the 6428-LSCF phase stability in modeling the stoichiometric changes to rhombohedral LSCF in the cell. Together this allows us to achieve spatial mapping, phase progression over time, and predict stoichiometry changes in early onset degradation. These methods identify several unique phases that result from the degradation of LSCF some of which are known to impact cell lifetimes. Identifying the pathways of early onset degradation allows for mitigation strategies to be developed for cell sintering and fabrication. (1) Hydrogen Shot. Energy.gov. https://www.energy.gov/eere/fuelcells/hydrogen-shot (accessed 2024-04-18). (2) Laguna-Bercero, M. A. Recent Advances in High Temperature Electrolysis Using Solid Oxide Fuel Cells: A Review. J. Power Sources 2012, 203, 4–16. https://doi.org/10.1016/j.jpowsour.2011.12.019. (3) Elder, R.; Cumming, D.; Mogensen, M. B. Chapter 11 - High Temperature Electrolysis. In Carbon Dioxide Utilisation; Styring, P., Quadrelli, E. A., Armstrong, K., Eds.; Elsevier: Amsterdam, 2015; pp 183–209. https://doi.org/10.1016/B978-0-444-62746-9.00011-6. (4) Ferrero, D.; Lanzini, A.; Santarelli, M.; Leone, P. A Comparative Assessment on Hydrogen Production from Low- and High-Temperature Electrolysis. Int. J. Hydrog. Energy 2013, 38 (9), 3523–3536. https://doi.org/10.1016/j.ijhydene.2013.01.065. (5) Hauch, A.; Jensen, S. H.; Ramousse, S.; Mogensen, M. Performance and Durability of Solid Oxide Electrolysis Cells. J. Electrochem. Soc. 2006, 153 (9), A1741. https://doi.org/10.1149/1.2216562. (6) Kanae, S.; Toyofuku, Y.; Kawabata, T.; Inoue, Y.; Daio, T.; Matsuda, J.; Chou, J.-T.; Shiratori, Y.; Taniguchi, S.; Sasaki, K. Microstructural Characterization of SrZrO3 Formation and the Influence to SOFC Performance. ECS Trans. 2015, 68 (1), 2463. https://doi.org/10.1149/06801.2463ecst. (7) Mogensen, M. B.; Chen, M.; Frandsen, H. L.; Graves, C.; Hauch, A.; Hendriksen, P. V.; Jacobsen, T.; Jensen, S. H.; Skafte, T. L.; Sun, X. Ni Migration in Solid Oxide Cell Electrodes: Review and Revised Hypothesis. Fuel Cells 2021, 21 (5), 415–429. https://doi.org/10.1002/fuce.202100072. (8) Tai, L.-W.; Nasrallah, M. M.; Anderson, H. U.; Sparlin, D. M.; Sehlin, S. R. Structure and Electrical Properties of La1 − xSrxCo1 − yFeyO3. Part 2. The System La1 − xSrxCo0.2Fe0.8O3. Solid State Ion. 1995, 76 (3), 273–283. https://doi.org/10.1016/0167-2738(94)00245-N. (9) Lu, Z.; Darvish, S.; Hardy, J.; Templeton, J.; Stevenson, J.; Zhong, Y. SrZrO3 Formation at the Interlayer/Electrolyte Interface during (La1-xSrx)1-δCo1-yFeyO3 Cathode Sintering. J. Electrochem. Soc. 2017, 164 (10), F3097. https://doi.org/10.1149/2.0141710jes.

Solid-oxide electrolyzer cells (SOECs) based on yttria-stabilized zirconia (YSZ) oxide electrolytes are devices capable of producing hydrogen with excess thermal energy. However, beginning with initial materials sintering and extending through electrochemical aging, Sr diffusion within the Gd-doped CeO2 (GDC) barrier layer has been observed to lead to the formation of unwanted secondary phases such as SrO and SrZrO3. To establish the impact of these phases on SOEC performance, we perform firstprinciples calculations to determine secondary phase bulk oxide conductivities and compared them to that of the YSZ electrolyte. We find that SrO has a low conductivity arising from poor mobility and a low concentration of oxygen vacancies (V_O^2+), and its presence in SOECs should therefore be avoided as much as possible. SrZrO3 also has a lower oxide conductivity than YSZ; however, this discrepancy is primarily due to lower V_O^2+ concentrations, not V_O^2+ mobility. We find Y-doping to be a viable strategy to increase V_O^2+ concentrations in SrZrO3, with 16% substitution of Y on the Zr site leading to an ionic conductivity on par with that of YSZ. Energy dispersive x-ray spectroscopy obtained using scanning transmission electron microscropy on cross-sections of SOECs indicates that Y is the most common minority element present in SrZrO3 forming near the GDC—YSZ interface. Thus, we expect SrZrO3 to be rich in V_O^2+ and not to hinder long-term device performance. These results from our combined computational–experimental analysis can inform future materials engineering strategies designed to limit the detrimental effects of Sr-induced secondary phase formation on SOEC performance.

All-solid-state batteries (ASSB) are a promising alternative to their conventional liquid electrolyte-based counterparts due to their increased safety and their potential to achieve higher energy density. To achieve these goals, a ASSB requires a solid-state electrolyte (SSE) with high ionic conductivity near room temperature and high electrochemical stability. Lithium and sodium salts of boron cluster anions have attracted much attention as SSE candidates due to their high ionic conductivities (>103 S/cm) following a solid-phase transition into a disordered phase at relatively low temperatures (50-130°C) and relatively wide electrochemical window.[1] In considering their application to ASSB, their mechanical properties also play a critical role due to the stresses the electrolyte material is subjected to during battery operation.[2] First-principle calculations have been instrumental so far to provide an initial assessment of bulk and elastic moduli for some selected boron cluster solid electrolytes,[3-5] but direct measurements are still lacking. Herein, we will report the first determination of elastic moduli and hardnesses of the most representative boron cluster salts using both nanoindentation continuous stiffness method (CSM) and ultrasound under inert atmosphere and compared with DFT calculations. References [1] R. Mohtadi et al., Nat. Rev. Mater., 2, 16091 (2017) [2] S. Kalnaus et al., Science, 381, eabg5998 (2023) [3] H. Chen et al., J. Electrochem. Soc., 166, A493 (2019). [4] Z. Lu et al., Chem. Mat., 29, 9308 (2017) [5] R. Moury et al., Acta Crystallogr., Sect. B: Struct. Sci., 75, 406 (2019)

Hydrogen incorporation in native surface oxides of metal alloys often controls the onset of metal hydriding, with implications for materials corrosion and hydrogen storage. A key representative example is titania, which forms as a passivating layer on a variety of titanium alloys for structural and functional applications. These oxides tend to be structurally diverse, featuring polymorphic phases, grain boundaries, and amorphous regions that generate a disparate set of unique local environments for hydrogen. Here, we introduce a workflow that can efficiently and accurately navigate this complexity. First, a machine learning force field, trained on ab initio molecular dynamics simulations, was used to generate amorphous configurations. Density functional theory calculations were then performed on these structures to identify local oxygen environments, which were compared against experimental observations. Second, to classify subtle differences across the disordered configuration space, we employ a graph-based sampling procedure. Finally, local hydrogen binding energies are computed using exhaustive density functional theory calculations on representative configurations. We leverage this methodology to show that hydrogen binding energetics are described by local oxygen coordination, which in turn is affected by stoichiometry. Together these results imply that hydrogen incorporation and transport in TiO_x can be tailored through compositional engineering, with implications for improving performance and durability of titanium-derived alloys in hydrogen environments.

All-inorganic CsPbI3 perovskite has emerged as a promising candidate for next-generation solar cells. However, owing to the poor structural stability of black phase CsPbI3 perovskite at room temperature, it spontaneously transforms to the yellow, photoinactive, nonperovskite phase at room temperature, limiting further development of CsPbI3 perovskite solar cells. To better understand the mechanism driving such undesirable phase transformation, we examine the thermodynamics and kinetics associated with gamma-to-6 phase transformation using density functional theory calculation. A solid-state nudged elastic band method was employed to find minimum energy pathways assuming a concerted solid-state phase transformation between these two phases. The gas molecules representing atmospheric (H2O, O2, and N2) and inert (Ar) ambient environments, as well as applied external pressure, were considered to examine the influence of external conditions on the black-to-yellow phase transition. Our calculation reveals that, with increasing pressure, the thermodynamic driving force for converting the gamma-phase to the 6-phase increases, whereas a larger activation energy must be overcome for the phase transition to occur. We also investigate the moisture-induced phase transformation with an H2O molecule and its dissociated species (H+/OH-) and demonstrate that the reaction energy barriers can be significantly lowered in the presence of H2O or OH-. On the other hand, other nonpolar species (O2, N2, and Ar) have a negligible effect on the phase transformation kinetics, while they might reduce the thermodynamic driving force for the phase transformation and suppress the undesirable phase transformation. Our theoretical prediction could support recent observations that the gamma-to-6 phase transformation occurs rapidly and catalytically in the presence of moisture, whereas in dry argon and dry oxygen atmospheres, the gamma-CsPbI3 remains stable.

Intercalation pseudocapacitance can combine capacitor-like power densities with battery-like energy densities. Such surface-limited behavior requires rapid diffusion where amorphization can increase solid-state diffusivity. Here intercalation pseudocapacitive materials with tailored extents of amorphization in T-Nb2O5 are first reported. Amorphization was characterized with WAXS, XPS, XAFS, and EPR which suggested a peroxide-rich (O-2(2-)) surface that was consistent with DFT predictions. A series of tunable isomorphic architectures enabled comparisons while independently varying transport parameters. Through process of elimination, solid-state lithium diffusion was identified as the dominant diffusive-constraint dictating the maximum voltage sweep rate for surface-limited kinetics (v(SLT)), termed the Surface-Limited Threshold (SLT). The v(SLT) increased with amorphization however stable cycling required crystalline T-Nb2O5. A current-response model using series-impedances well-matched these observations. This perspective revealed that amorphization of T-Nb2O5 enhanced solid-state diffusion by 12.2 % and increased surface-limitations by 17.0 % (stable samples). This approach enabled retaining 95 % lithiation capacity at similar to 800 mV s(-1) (1,600 C-rate equivalent).

Titanium (Ti) and its alloys are attractive for a wide variety of structural and functional applications owing to excellent specific strength, toughness and stiffness, and corrosion resistance. However, if exposed to hydrogen sources, these alloys are susceptible to hydride formation in the form of TiHx (0 < x & LE; 2), leading to crack initiation and mechanical failure due to lattice deformation and stress accumulation. The kinetics of the hydriding process depends on several factors, including the critical saturation threshold for hydrogen within Ti, the specific interaction of hydrogen with protective surface oxide, the rates of mass transport, and the kinetics of nucleation and phase transformation. Unfortunately, key knowledge gaps and challenges remain regarding the details of these coupled processes, which take place across vast ranges of time and length scales and are often difficult to probe directly. This work reviews recent advances in multiscale characterization and modeling efforts in Ti hydriding. We identify unanswered questions and key challenges, propose new perspectives on how to solve these remaining issues, and close knowledge gaps by discussing and demonstrating specific opportunities for integrating advanced characterization and multiscale modeling to elucidate chemistry and composition, microstructure phenomena, and macroscale performance and testing.

Understanding hydrogen transport is vital to industries focused on discovering new materials for energy storage and corrosion mitigation. However, knowledge of the physical nature of hydrogen’s diffusion pathways is often limited, especially for materials that exhibit a multitude of phases/defect classes. These materials typically have three rate-limiting structural domains: (1) bulk (2) grain boundaries, and (3) surfaces. In this work we have chosen to study hydrogen diffusion through titania due to its importance in the aforementioned application spaces. Here, we aim to understand diffusion through titania grain boundaries, which are approximated via the amorphous phase. Density functional theory (DFT) was used to calculate thousands of activation energies of hydrogen diffusion in the amorphous phase via nudged elastic band calculations using an automated hydrogen pathway generation scheme. Amorphous structures, on the order of tens of nanometers, were generated using a machine learning force field via classical molecular dynamics (MD). Markov chains were generated using the MD-derived atomic structures as their reference. Kinetic Monte Carlo (KMC) simulations were then performed over a variety of temperatures and stoichiometries, for system sizes in the tens of nanometers, allowing us to connect directly with experimental measurements. Using our KMC simulations we can directly calculate the hydrogen diffusion constant, as a function of temperature and stoichiometry, and compare these values with those determined via experiments. We also employ a graph-based characterization scheme that can quantify the subtle differences in local hydrogen diffusion networks throughout the KMC simulation, allowing us to link local hydrogen diffusivity with structural differences within the material observed along the diffusion pathway. This work sets the stage for one to perform long time-scale and/or length-scale simulations to understand how temperature and atomic structure affect properties such as diffusivity, solubility, and permeation, and connect these values directly with experiments.

Hydrogen interaction with metal oxides is an important phenomenon that affects all vital areas of industry such as aerospace, transportation, and commercial applications. The metal oxide provides a naturally forming protective layer against dissolution of the underlying metal. It has been reported that hydrogen is still able to percolate through this protective layer traveling all the way to the metal to form a corrosive brittle metal hydride. There have been many studies looking to understand the interaction of hydrogen at the surface but an in depth look at the surface to bulk transition of hydrogen through a metal oxide for all representative phases of an oxide is minimally represented in the literature. For the focus of our study, we employed a multi-scale approach combined with experimental studies to explore the different phases of titania (TiO2) which includes rutile, anatase, and an amorphous phase. A thermodynamic analysis of the stability for hydrogen was considered using density functional theory (DFT) starting at the low energy surface facets to the bulk. For the amorphous phase, the binding energy was analyzed as a function of the hydrogen content and oxygen coordination environment. Temperature programmed desorption (TPD) experiments provided a direct comparison with theory. Additionally, NMR simulations validified the generated amorphous phase which agreed well with experimental data. The material properties computed using DFT were used in combination with experimental results to parameterize a mesoscale model. Several environmental conditions were analyzed consisting of grain size, temperature, and grain boundary properties. Further work investigated crystalline titanium (Ti) in the bulk and at several grain boundaries to elucidate possible initiation stages of hydride formation. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Colloidal semiconductor nanocrystals are important building blocks for low-cost, solution-processed electronic devices with tunable functionalities. Considerable progress is made in improving charge transport through nanocrystal films by exchanging long insulating ligands with shorter passivating ligands. To take full advantage of this strategy, it is equally important to fabricate close-packed structures that reduce the average interparticle spacing. Yet it remains a challenge to retain long-range, close-packed order after ligand exchange. Here, a novel one-step in situ ligand-exchange method is demonstrated that enables rapid (5 min) ligand exchange of nanocrystal films, which are more than 50 layers thick. Using this simple and efficient method, it is shown that the face-centered cubic ordering of 500 nm thick PbSe nanocrystal films is retained after ligand exchange from oleic acid to benzoic acid. Moreover, it is demonstrated that PbSe nanocrystal photodetectors with a well-ordered structure have superior optoelectronic properties compared to disordered films; ordered films have a 16× higher responsivity of ≈0.25 A W-1 at 1 V and a 2× faster response time. As far as it is known, this is the first report to realize a rapid one-step ligand exchange through a thick superlattice film with retention of long-range order.

Reactive Ti-5Al-5 V-5Cr-3Mo (Ti5553) alloy feedstock powder is used in laser powder-bed fusion (LPBF). Due to the large quantity of powder necessary for LPBF, powder is reused numerous times under oxidizing environments. Transformations to the powder's native surface oxide may impact the LPBF process and lead to deviations from expected behavior of printed parts. Here, we present a multimodal characterization of new and reused powder by combining X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), and transmission electron microscopy (TEM) of focused ion beam (FIB)-prepared cross sections of individual powder particles to understand how the surface oxide composition changes, grows, and becomes hydroxylated and hydrated due to reuse. We show that the native oxide film of Ti5553 powder is a hydroxylated mixed oxide composed of TiO2 and Al2O3 that grows from 5.6 +/- 0.7 nm to 8.3 +/- 1.1 nm due to reuse. Al oxide regions of the surface oxide become more hydroxylated during reuse in comparison to Ti oxide regions. This indicates that an outer oxide of pure TiO2 may enhance recyclability of Ti5553 powder while the presence of Al oxides may decrease recyclability. Further characterization of surface transformations due to recyclability may eliminate unnecessary variation in LPBF.